The overall aim of this project is to determine whether a special formulation of orthophosphate (slow-release neutral potassium phosphate or Uro-Phos-K would correct hypercalciuria, prevent recurrent stone formation and provide safety of usage in hypercalciuric nephrolithiasis. In a controlled randomized trial, the effect of Uro-Phos-K will be compared with those of Urocie-K (potassium citrate) in hypercalciuric patients with recurrent nephrolithiasis. The hypothesis to be tested is that UroPhos-K unlike Urocie-K would lower urinary calcium, and would be more effective that Urocie-K in inhibiting new stone formation.